The present invention disclosed herein relates to a variable gain amplifier capable of automatically adjusting the magnitude of a signal, and more particularly, to a variable gain amplifier having a high dynamic range and a receiver including the same.
The present invention has been derived from research undertaken as a part of IT R & D program of the Ministry of Information and Communication and Institution of Information Technology Association (MIC/IITA) [2005-S-017-03], Integrated development of ultra low power RF/HW/SW SoC.
In various application fields such as disk drivers, hearing aids, medical equipment, and optical receivers, a variable gain amplifier (VGA) is an indispensable device block. Especially, the VGA is required to provide a high gain in order to reduce noise in a low signal power while signal environments are exposed to noise, and also to provide a low gain in order not to worsen distortion when a receiving signal is inputted at the maximum power, in a mobile communication system. To this end, the VGA needs to have a high dynamic range in which a variable gain range is possible. Only so, a digital signal processor (DSP) can stably demodulate a received signal to an original signal.
The VGA using a bipolar junction transistor (BJT) with characteristics of an exponential function is typically used to provide a voltage gain of a decibel (dB) unit, which is proportional to a control voltage. However, because of demands for a complementary metal oxide semiconductor (CMOS) system-on-chip (SoC) and circuit technology developments, the VGA having characteristics of an exponentially linear gain is currently realized as a CMOS device. However, because this CMOS VGA requires a plurality of device blocks to achieve characteristics of an exponentially linear gain, its structure becomes very complex and requires high power consumption. Most of all, the CMOS VGA, because it is a high gain amplifier, is extremely vulnerable if design variables change during manufacturing processes, and thus its design value characteristics can be sensitively changed and greatly deteriorated. Moreover, although a chip of the CMOS VGA can be perfectly realized, frequency or gain characteristics can be deteriorated when a chip temperature changes.